Discovery of Stereospecific PARP-1 Inhibitor Isoindolinone NMS-P515

Abstract

Poly(ADP-ribose) polymerase-1 (PARP-1) is an enzyme involved in signaling and repair of DNA single strand breaks. PARP-1 employs NAD⁺ to modify substrate proteins via the attachment of poly(ADP-ribose) chains. PARP-1 is a well established target in oncology, as testified by the number of marketed drugs (e.g., Lynparza, Rubraca, Zejula, and Talzenna) used for the treatment of ovarian, breast, and prostate tumors. Efforts in investigating an uncharted region of the previously identified isoindolinone carboxamide series delivered (S)-13 (NMS-P515), a potent inhibitor of PARP-1 both in biochemical (K _d: 0.016 μM) and cellular (IC₅₀: 0.027 μM) assays. Cocrystal structure allowed explaining NMS-P515 stereospecific inhibition of the target. After having ruled out potential loss of enantiopurity in vitro and in vivo, NMS-P515 was synthesized in an asymmetric fashion. NMS-P515 ADME profile and its antitumor activity in a mouse xenograft cancer model render the compound eligible for further optimization.

Figure 1

Marketed PARP-1 inhibitors (1–4) and isoindolinone carboxamide derivatives (5–7).

Scheme 1. Synthesis of Compound (±)-13

Reagents and conditions: (a) 4-amino-piperidine-1-carboxylic acid tert-butyl ester, 1 M TiCl₄ in DCM, TEA, DCM, reflux, then NaCNBH₃, MeOH, rt, 80%; (b) maleic anhydride, toluene, reflux, 6 h, 80%; (c) 37% HCl, reflux, 70%; (d) di-tert-butyl dicarbonate, K₂CO₃, pyridine, MeOH, rt, 78%; (e) HOBt·NH₃, EDCI·HCl, DIPEA, DMF, rt, 75%; (f) 4 M HCl in dioxane, 50 °C; (g) cyclohexanone, NaCNBH₃, NaOAc, DCM/MeOH, rt, 76%.

Scheme 2. Synthesis of Compound (±)-18

Reagents and conditions: (a) NBS, Bz₂O₂, methyl pivalate, reflux then 1-cyclohexyl-piperidine-4-ylamine, TEA, acetonitrile, reflux, 40%; (b) MeI, NaHMDS 1 M in THF, rt, 90 min; (c) CuCN, DMF, reflux, 90 min, 54%; (d) 37% HCl, 100 °C then HOBt·NH₃, EDCI·HCl, DIPEA, DMF, rt, 38%.

Figure 2

Cocrystal structure of (S)-13 (NMS-P515, blue, top left) and (R)-13 (green, top right) with chicken PARP-1 CD and their overlapping (bottom).

Figure 3

(A) ArrayScan Images of HeLa cells treated with dimethyl sulfoxide (DMSO, control), and same concentration (0.37 μM) of (±)-13 (NMS-P515) and (R)-13 followed by hydrogen peroxide-induced PAR formation (blue, Hoechst (DNA); green, antibody anti-PAR). (B) Tumor growth inhibition of Capan-1 pancreatic cancer xenograft model (control, blue line; NMS-P515, purple line; Temozolomide, green line; NMS-P515 + Temozolomide, red line).

Scheme 3. Asymmetric Synthesis of NMS-P515

Reagents and conditions: (a) 1-cyclohexyl-piperidin-4-one, 1 M TiCl₄, DCM, then NaCNBH₃, MeOH, 52%; (b) maleic anhydride, toluene, 110 °C; (c) 37% HCl, 100 °C; (d) HOBt·NH₃, EDCI·HCl, Et₃N, THF, 40%.